This invention relates to a stator winding drive circuit for a reversible, brushless d.c. motor, particularly adapted for use in a magnetic recording tape deck.
In conventional d.c. motors having a mechanical commutator, it is easily possible to selectively produce a forward or a reverse torque by merely changing the polarity of the commutator voltage. However, d.c. motors of this type have an inherent disadvantage in that considerable noise is produced by the mechanical commutator, which adversely affects other equipment around the motor.
In order to resolve this defect, a brushless d.c. motor has been developed which employs Hall elements for detecting the rotor position and semiconductor switching elements responsive to the detection of the rotor position to switch the electric currents supplied to the windings of the motor. That is, the combination of the Hall elements and the semiconductor switching elements serves the same general function as the mechanical commutator. Since this construction has no mechanical components, there is no possibility of noise generation.
Such a brushless d.c. motor has been successfully used. However, since most semiconductor switching elements cannot accomodate a current flow in both directions, it is very difficult to design a simple and effective semiconductor switching circuit which can selectively provide bidirectional currents to thereby produce reversible motor torques.